The present invention relates to an improved fluid actuated gate valve with a manual override.
Prior to the present invention there have been gate valves of the type contemplated herein which included a fluid actuator and a valve member which moved axially responsive to the movement of a pressure responsive piston which causes the rotation of a stem and the stem rotation is translated into the axial movement of the gate. Such valves are often used in high pressure applications (e.g., 10,000 psi operating pressure) and in small sizes (e.g., one-half inch size). Since such pressure responsive actuators may have a pressure fluid trapped therein when it is desired to manually move the gate they have not been movable without bleeding the operator chambers.
U.S. Pat. No. 4,189,950 discloses a manual override apparatus to be used as a valve actuator which includes a threaded stem extending through the manual override housing and a pair of nut halves which are connected to a crank mechanism through a camming system which causes the nuts to move into engagement with the threaded stem when the crank handle is rotated.
Overrunning clutches are well known and include a plurality of sprags or paddles which are positioned between two cylindrical surfaces and when they are rotating in one direction with respect to each other both are freewheeling and when the reverse direction is used by the driving surface the paddles provide the engagement with the driven surface to cause rotation thereof.